As is well known, cold forging various industrial parts is one of several forging techniques available to the artisan. In certain instances, it offers particular advantages over hot forging techniques, for example, because it includes less expensive billet preparation and eliminates post-forging processes such as descaling and the like. On the other hand, cold forging requires substantially higher forging forces to cause the metal to flow through the forging die. This produces significant stresses on the forging die itself and thus creates significant limitations on the process itself, including low die life and premature breakage. This is particularly true when forging helical gears, as opposed to spur gears, since the gear teeth are formed at an angle relative to the vertical axis of the die and this, in turn, produces a reaction force perpendicular to the axis of the forging die teeth which results in significant bending stresses and resultant early die failure. Particularly, this may result in the die teeth shearing at the lead end of the die as a result of substantial bending stresses.
It is known that these bending stresses can be reduced by allowing the die, or die punch, or both, to freely rotate during the forging stroke about the vertical axis of each. This reduces stress on the entire die and consequently on the lead end of the die teeth.
It is also known, as shown in U.S. Pat. No. 5,052,210, assigned to the assignee of the present invention, that the effect of this compressive force may be controlled by providing a compound angle at the lead end face of the die teeth such that one end face land constituting at least a major portion of the land is perpendicular to the helix and the remaining end face land is perpendicular to the die axis.
Beyond the above mentioned teachings, the art of reducing or controlling compressive flows produced by forging, in the production of cold forge gear blanks having internal or external gear teeth through careful gear design, is not well known.